The Main and Tiree study was the first of four separate cardiorespiratory cohort studies that were carried out in Scotland, United Kingdom, in the 1960s and 1970s, known collectively as the Midspan studies. The 'Main' study took place between 1964 and 1968 and included nearly 4,000 factory employees (3,417 males, 514 females) aged 15 to 70 years, who were recruited from thirteen factories throughout the central belt of Scotland. The Tiree study began in May 1967 with the aim of recording the health details of all residents of the island of Tiree aged over 15. In total, 532 islanders took part in this study, and later, 230 of their relatives who had settled on the mainland were also recruited into the study in 1968. Participants in both the Main and Tiree cohorts completed the same questionnaire and screening examinations at baseline and were followed up 2-4 years later with the same examinations as well as with ongoing linkage to mortality data.